Moulds are known comprising a pair of dies or inserts of half moulds, suitable for forming by moulding elements such as, for example, preforms or parts of preforms, generally provided with projecting portions or undercuts, which constitute portions of bottle necks or other containers. The portions of bottle necks made of plastics in fact have projections comprising a fitting thread for a corresponding cap and an annular collar.
At the end of moulding, the preform remains in the mould for a certain period of time so as to cool and consolidate the shape thereof. Subsequently, the preform is extracted from the mould, by removing the two dies from one another so as to free the undercuts.
The preform has to be cooled in a sufficiently rapid manner to reduce moulding time and ensure high production speed.
To cool the preforms, the dies are provided with a circuit through which a cooling fluid flows. The circuit generally comprises a plurality of rectilinear conduits, made by mechanical drilling operations with machine tools. The conduits are generally arranged on a single level and are intersected amongst themselves to form the circuit through which the cooling fluid flows.
In the case of dies that, in a closed configuration, define a cavity delimited by a substantially cylindrical forming surface, the rectilinear conduits are arranged tangentially to this cavity. Thus, adjacent zones of the forming surface are at distances that are different from one another from the rectilinear conduits and are not uniformly cooled by the cooling fluid.
Caps for bottles or containers are known comprising a cup body delimited by a cylindrical side wall, provided with an inner threaded surface closed at an end thereof by a bottom wall. A sealing lip is projected from the bottom wall to the inside of the cup body. During use, the sealing lip engages with an edge of the container so that the container is closed in a substantially hermetic manner.
The caps of the disclosed type are obtained inside moulds comprising a die provided with a forming cavity and a punch interacting with the die to form plastics in fluid or semifluid state so as to form the cap. The sealing lip is formed together with the cup body and the whole of the cup body and the sealing lip constitutes a single piece. If the sealing lip has undercut zones, in order for detaching the cap from the punch, the latter is made of two parts and comprises a central element and an outer element that can move with respect to the central element so as to remove the cap that has already been formed from the central element.
The moulds for closing caps of the type disclosed above are provided with circuits through which a cooling fluid can flow, that enables the cap to be cooled before the cap is extracted from the mould. This circuits are realized both in the die and in the central element of the punch.
A drawback of known moulds arranged for making caps is that they do not enable efficient and rapid cooling from the inside of the cap, in particular at the threaded surface of the cap and at the sealing lip. This drawback enables the cooling time to be increased and therefore the duration of the moulding cycle to be increased, with a reduction in production speed.